1. Field of the Invention
This invention relates to method and apparatus for marking an object by imprinting characters on an arcuate surface of the object and more particularly to apparatus for simultaneously imprinting on the arcuate surface of an object indented dot portions of selected characters to simultaneously form the characters on the arcuate surface.
2. Description of the Prior Art
The printing or engraving of alphanumeric characters on a workpiece, such as sheet material in the form of paper or the like, as well as machine parts, by dot matrix type computer controlled printing is well known. U.S. Pat. Nos. 4,306,497 and 4,446,789 are examples of dot matrix type printers operable to perform high speed printing of various types of characters in the output of computer generated printing for use with data and word processing systems. These types of printers include a plurality of print elements of the dot type each having a single impact wire for printing dots on a sheet of paper which is vertically fed opposite the printer head after each line of printing is formed on the paper.
U. K. Patent No. 2,002,694 discloses an engraving machine for a dot matrix printing on machine parts, utilizing a single impact tool or punch mounted on a carriage for movement in a raster pattern along a X-axis and a Y-axis. The punch impacts the workpiece to form alphanumeric characters from a selected array of dots impressed on the surface of the workpiece. The engraver is computer controlled to provide selective continuous marking of the workpiece in a raster pattern. The surface of the workpiece to be marked is maintained in a horizontal plane and stationary relative to the punch. The punch is moved in the raster pattern to imprint the selected array of dots on the horizontal surface to generate the desired alphanumeric characters on the workpiece.
U.S. Pat. No. 4,591,279 is a further example of a marking apparatus for imprinting alphanumeric characters in dot matrix form on production line items, such as slabs, rolled stock, plates, tags, and a variety of parts fabricated of material that includes glass, metal, and plastic. A marking head assembly includes a plurality of impact pins which are reciprocated into and out of contact with the flat planar surface of a workpiece by operation of computer programmable solenoid valves. An indexing wheel adjusts the angular position of the marking head assembly to control the size of the characters formed by the pins impacting the workpiece. The marking head assembly is pivotally mounted on a plate. A ball screw drive connects the plate to a frame for imparting longitudinal movement to the plate as the marking head assembly imprints a plurality of dots in a preselected array on the surface the workpiece to form the desired alphanumeric characters.
It is also known to impress a preselected array of dots on the surface of an object having an arcuate contour. U.S. Pat. No. 4,848,942 discloses marking apparatus for imprinting dot matrix characters on the arcuate surface of a cylindrical object. The cylindrical object is rotatably supported by rollers, and a driver roll controls the rate of rotation of the object. A plurality of marking pins are positioned in a fan-shaped array around the periphery of the arcuate surface of the object to be marked. Each marking pin is reciprocally supported and actuated by an electrically operated solenoid to extend and retract to indent the surface of the object with a dot. The object is rotated relative to the plurality of fixed marking pins. The pins are selectively actuated to imprint a preselected array of dot matrix characters around the circumference of the arcuate object.
Electric solenoids are selectively programmed for operation to extend and retract the pins in a controlled manner to indent the object with dots to form a single line dot matrix array of characters. As disclosed in U.S. Pat. No. 4,848,942 each pin is set at a different level and each pin forms a different row of dots. The spacing between the rows of dots determines the height of the characters being formed. Accordingly, the marking pins are adjustable on a marking head assembly to adjust the height of the characters. The object rotates 360.degree. plus the length of the marking head assembly in order to imprint characters around the complete circumference of the object.
While it is known to imprint dot matrix type characters on a surface of a workpiece and particularly the arcuate contour of a workpiece, the known devices utilize a plurality of impact markers to form rows of dots in a preselected array to form the desired characters on the surface of the object. Each impact marker is used to form the required dots in a specific row. As disclosed in U.S. Pat. No. 4,848,942, the marking pins must be set on different levels so that the rows of dots are spaced a preselected distance apart to provide the required height for the characters formed by the composite array of dots. Accordingly, the marking pins must be precisely mounted to assure the required spacing between rows of dots. If the height of the characters is to be adjusted, then the position of each marking pin must be adjusted on the marking head assembly.
Adjustments in the positioning of the marking pins and maintaining the required position of the pins substantially adds to the complexity of the marking head assembly. Also, in order to form characters around the complete circumference of the object, the object must be moved through 360 degrees while the marking pins remain stationary relative to the rotating object. In order to print a row of dots the object must be rotated over one complete revolution. This method of forming characters around the circumference of an arcuate shaped object where the object moves relative to the fixed marking pins is more time consuming than desired.
Therefore, there is need in the marking of dot matrix type characters on the arcuate surface of an object for a marking device that utilizes a plurality of impact markers to form an array of dots on the arcuate surface. The imprinting of the dots needs to be accomplished without requiring the object to rotate through a complete revolution. The impact markers should be efficiently mounted on a marking head so as not to require individual adjustment of the position of each impact marker. There is need for an arrangement permitting the position of the impact markers to be adjusted relative to the object by a single adjustment of the marking head assembly so that the rows of dots forming the characters are spaced an equal distance apart.